GB2239522A

GB2239522A - A linear displacement sensor

Info

Publication number: GB2239522A
Application number: GB8929212A
Authority: GB
Inventors: Alan David Brunning
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1989-12-27
Filing date: 1989-12-27
Publication date: 1991-07-03
Also published as: GB8929212D0

Abstract

A linear displacement sensor makes use of a known flexible, force and position sensing linear potentiometer (Fig. 1) and bonds this potentiometer into a U-shape before mounting the opposite ends on components 28, 32 which are linearly movable relative to one another. As the components move, the fold between two arms of the U-shape is forced to roll along the length of the potentiometer and this causes the point of electrical contact to move at the same time. <IMAGE>

Description

A LINEAR DISPLACEMENT SENSOR This invention relates to a linear displacement sensor for sensing the relative positions of two components which are relatively moveable in a linear direction.

According to the invention, there is provided a linear displacement sensor in the form of a flexible, force and position sensing linear potentiometer bent into a U-shape and with one end secured to a first component and the other end secured to a second component which is linearly moveable relative to the first component.

The potentiometer is preferably of the type sold by Interlink Electronics of 535 E. Montecito Street, Santa Barbara, California 93103, USA and referred under the trade mark 'FSR' (FSR stands for force sensing resistor). The properties of these force sensing resistors are described in detail in Applications Note IL-O1 issued by Interlink Electronics, but those aspects of the properties which are relevant to this invention will be described again here.

Force sensing resistors can be used as linear potentiometers by applying a force to the resistor at any point along its length. The force may typically be applied by a human finger and in this way the resistor acts as a touch-sensitive potentiometer. This property can then be used to control an electronic or mechanical device.

The application of force produces an electrical contact between two lamina components which are printed with conducting tracks, and as a result a conducting path is formed through the point on the resistor where the force is applied. Varying the position of application of the force changes the resistance.

The applicants have now found that in place of a direct application of force to a particular point on the resistor, the same effect can be produced by bending the resistor into a U-shape which results in the respective laminae being forced into contact at the bend of the U. If the ends of the resistor are then moved linearly relative to one another so that the bend in the U is rolled along the length of the resistor, then the point of contact changes and the apparent resistance changes. A practical use can be made of this feature by mounting the ends of the resistor on components which are relatively moveable in a linear direction. The voltage read from the resistor is thus representative of the relative position of the two components.

This property of the resistor can be used in many applications, but two possible automotive applications are to monitor the movement occurring in suspension dampers, or the movement occurring in a steering rack.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an exploded view of a force sensing resistor forming a linear potentiometer; Figure la is an electrical representation of the potentiometer; Figure 2 is a sectional view through an assembled linear potentiometer; and Figure 3 illustrates a linear displacement sensor in accordance with the invention.

Figure 1 shows the two laminae which make up the resistor.

These laminae are a fixed resistor strip 10 and a force sensing layer 12. The resistor strip 10 is in the form of a flexible plastics strip with, printed onto one face, a resistive area 14 and two sets of conductive tracks 16a and 16b. Two connector leads 18 and 20'apply a voltage along the resistive area 14. In one of the sets of tracks, the tracks 16a are in electrical connection with the strip 14.

A voltage reading connection 22 is connected to the other set of conductive strips 16b which are intercalated with the tracks 16a.

The force sensing layer 12 is mounted on another flexible plastics strip and is placed against the printed side of the resistor strip, but there is no direct connection between the two layers. However when an external force is applied to the resistor strip, an electrical connection is made between a track 16a and a track 16b, through the coating on the force sensing layer, and as a result a voltage reading is produced on the connection 22. The magnitude of this voltage will depend on the distance along the strip 14 at which this connection is made. The magnitude of the voltage sensed at 22 will depend both on the position at which force is applied and, as a result of the construction of the force sensing layer 12, on the magnitude of the force which is applied.For present purposes- however the applied force will be substantially constant and we are just interested in the position at which the force sensing layer is forced into contact with the conductive tracks 16a, 16b.

The laminae 10 and 12 are provided on flexible substrates and are then encased in a sealed envelope 24 (Figure 2).

The connections 18, 20, 22 will be taken out from this envelope at convenient points.

In accordance with the invention, the force sensing resistor is bent into a U-shape as shown in Figure 3. One end 26 is connected to a fixed component 28 and the other end of the resistor 30 is connected to a moveable component 32. As the component 32 moves in the direction of the arrow 34, the bend 36 of the U-shape will roll along the length of the strip, and consequently the point along the strip at which the electrical contact is made will also move along the strip. Monitoring the voltage on the output 22 will therefore provide an indication of the relative movement of the components 28 and 32.

Claims

1. A linear displacement sensor in the form of a flexible, force and position sensing linear potentiometer bent into a U-shape and with one end secured to a first component and the other end secured to a second component which is linearly moveable relative to the first component.

2. A sensor as claimed in Claim 1, wherein the potentiometer is of the type sold by Interlink Electronics of 535 E. Montecito Street, Santa Barbara, California 93103, USA and referred under the trade mark 'FSR'.

3. A linear displacement sensor substantially as herein described with reference to the accompanying drawings.